The present disclosure relates generally to gaskets and, more particularly, to dual barrier gaskets.
Gaskets are commonly used in a number of industries for sealing a variety of equipment, such as valves. In the production of oil and gas in the field, a number of valves are often used with a well tree at a well head to control fluid flow associated with the well. Another valve, such as a down-hole safety valve (DHSV), also known as a sub-surface safety valve (SSSV), is positioned down the well to provide closure under emergency conditions.
In subsea well applications, industry standards require at least two sealing barriers between the flow bore, which contains production fluid, and the exterior environment for openings located before the first wing valve of the subsea tree. This same requirement may also be imposed on surface equipment by customers. However, tree gate valve bonnet flanges and piping outlet flanges typically associated with well tree equipment are usually equipped with gaskets providing only a singly sealing barrier. In the past, to meet the two-barrier industry standard, some have considered the lower master valve at the well tree to be a second barrier, and the DHSV or SSSV has been considered to be the first barrier. But this design approach provides two sealing barriers only when the DHSV or SSSV is closed. When the DHSV or SSSV is open, the conventional gaskets of the well tree are the only barrier between the production fluid and the environment. Conventional gaskets only provide one barrier. In such conditions, that approach fails to meet the two-barrier standard and renders the well vulnerable to leakage and potentially disastrous events. Some have addressed this issue by adding a second outer gasket to the flange that encompasses a smaller inner gasket. This has the disadvantage that the larger, outer gasket will require a much large flange and flange retention means, such as bolting size or clamp size.